Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. In some examples, an apparatus for video decoding includes receiving circuitry and processing circuitry. According to an aspect of the disclosure, the processing circuitry decodes prediction information of a current block in a first coding tree unit (CTU) in a picture from a coded video bitstream. The prediction information is indicative of an intra block copy mode. The processing circuitry excludes reconstructed samples of a second CTU that is adjacent to a left side of the first CTU in the picture from being reference samples for a reconstruction of the current block. Then, the processing circuitry reconstructs samples of the current block based on reference samples that are in the picture and constrained with the exclusion of the reconstructed samples of the second CTU.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of priority to U.S.Provisional Application No. 62/698,518, “TECHNIQUES FOR CONSTRAINEDSEARCH RANGE IN INTRA PICTURE BLOCK COMPENSATION” filed on Jul. 16,2018, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 2 shows a schematic (201) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes receiving circuitry and processing circuitry. According to anaspect of the disclosure, the processing circuitry decodes predictioninformation of a current block in a first coding tree unit (CTU) in apicture from a coded video bitstream. The prediction information isindicative of an intra block copy mode. The processing circuitryexcludes reconstructed samples of a second CTU that is adjacent to aleft side of the first CTU in the picture from being reference samplesfor a reconstruction of the current block. Then, the processingcircuitry reconstructs samples of the current block based on referencesamples that are in the picture and constrained with the exclusion ofthe reconstructed samples of the second CTU.

In an example, the processing circuitry excludes the second CTU from areference area for providing the reference samples for thereconstruction of the current block.

In some embodiments, use padding samples to replace the reconstructedsamples of the second CTU as the reference samples for thereconstruction of the current block. In an embodiment, the processingcircuitry obtains the padding samples without waiting for thereconstructed samples of the second CTU to be stored to a first memoryfor storing reconstructed samples of the picture.

In some examples, the processing circuitry accesses the first memory forreconstructed samples of a neighboring CTU to the second CTU to obtainthe padding samples. In an example, the processing circuitry accessesthe first memory for a bottom row of reconstructed samples of an aboveneighboring CTU to the second CTU, and pads rows of the second CTUrespectively according to the bottom row of the reconstructed samples ofthe above neighboring CTU. In another example, the processing circuitryaccesses the first memory for a rightmost column of reconstructedsamples of a left neighboring CTU to the second CTU, and pads columns ofthe second CTU respectively according to the right most column of thereconstructed samples of the left neighboring CTU to the second CTU. Inanother example, the processing circuitry accesses a second memory thatbuffers a rightmost column of the second CTU, the second memory being anon-chip memory that has a faster access speed than the first memory thatis an off-chip memory, and pads columns of the second CTU respectivelyaccording to the rightmost column of the second CTU.

In some examples, the processing circuitry pads the second CTU usingconstant values.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a subset of intra prediction modesin accordance with some examples.

FIG. 2 is an illustration of intra prediction directions according tosome examples.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 6 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 7 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 8 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 9 shows an example of intra block copy according to an embodimentof the disclosure.

FIG. 10 shows an example of bilateral matching according to someembodiments.

FIG. 11 shows an example of template matching according to an embodimentof the disclosure.

FIG. 12 shows an example of spatial merge candidates.

FIG. 13 shows an example of excluding left CTU in the intra block copymode according to an embodiment of the disclosure.

FIG. 14 shows a diagram for padding pixel values of reference area inthe intra block copy mode according to an embodiment of the disclosure.

FIG. 15 shows a flow chart outlining a process example (1500) accordingto an embodiment of the disclosure.

FIG. 16 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 3 illustrates a simplified block diagram of a communication system(300) according to an embodiment of the present disclosure. Thecommunication system (300) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (350). Forexample, the communication system (300) includes a first pair ofterminal devices (310) and (320) interconnected via the network (350).In the FIG. 3 example, the first pair of terminal devices (310) and(320) performs unidirectional transmission of data. For example, theterminal device (310) may code video data (e.g., a stream of videopictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (330) and (340)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (330) and (340) via the network (350). Eachterminal device of the terminal devices (330) and (340) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (330) and (340), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 3 example, the terminal devices (310), (320), (330) and(340) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (350) represents any number ofnetworks that convey coded video data among the terminal devices (310),(320), (330) and (340), including for example wireline (wired) and/orwireless communication networks. The communication network (350) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(350) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 4 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (413), that caninclude a video source (401), for example a digital camera, creating forexample a stream of video pictures (402) that are uncompressed. In anexample, the stream of video pictures (402) includes samples that aretaken by the digital camera. The stream of video pictures (402),depicted as a bold line to emphasize a high data volume when compared toencoded video data (404) (or coded video bitstreams), can be processedby an electronic device (420) that includes a video encoder (403)coupled to the video source (401). The video encoder (403) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (404) (or coded video bitstream (404)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (402), can be stored on a streamingserver (405) for future use. One or more streaming client subsystems,such as client subsystems (406) and (408) in FIG. 4 can access thestreaming server (405) to retrieve copies (407) and (409) of the encodedvideo data (404). A client subsystem (406) can include a video decoder(410), for example, in an electronic device (430). The video decoder(410) decodes the incoming copy (407) of the encoded video data andcreates an outgoing stream of video pictures (411) that can be renderedon a display (412) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (404),(407), and (409) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows a block diagram of a video decoder (510) according to anembodiment of the present disclosure. The video decoder (510) can beincluded in an electronic device (530). The electronic device (530) caninclude a receiver (531) (e.g., receiving circuitry). The video decoder(510) can be used in the place of the video decoder (410) in the FIG. 4example.

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (501), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (531) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (531) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (515) may be coupled inbetween the receiver (531) and an entropy decoder/parser (520) (“parser(520)” henceforth). In certain applications, the buffer memory (515) ispart of the video decoder (510). In others, it can be outside of thevideo decoder (510) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (510), forexample to combat network jitter, and in addition another buffer memory(515) inside the video decoder (510), for example to handle playouttiming. When the receiver (531) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (515) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (515) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such as arender device (512) (e.g., a display screen) that is not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as was shown in FIG. 5. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (520) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (520) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (520). The flow of such subgroup control information between theparser (520) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values, thatcan be input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (558). The currentpicture buffer (558) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(555), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (552) has generated to the outputsample information as provided by the scaler/inverse transform unit(551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to the render device (512) as well as stored in the referencepicture memory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (510) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows a block diagram of a video encoder (603) according to anembodiment of the present disclosure. The video encoder (603) isincluded in an electronic device (620). The electronic device (620)includes a transmitter (640) (e.g., transmitting circuitry). The videoencoder (603) can be used in the place of the video encoder (403) in theFIG. 4 example.

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the FIG. 6example) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) is a part ofthe electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (601) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (601) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence into a coded videosequence (643) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (650). In some embodiments, the controller(650) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (650) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (650) can be configured to have other suitablefunctions that pertain to the video encoder (603) optimized for acertain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (634). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (634) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5. Brieflyreferring also to FIG. 5, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video coder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (640) may transmit additional datawith the encoded video. The source coder (630) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 7 shows a diagram of a video encoder (703) according to anotherembodiment of the disclosure. The video encoder (703) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (703) is used in theplace of the video encoder (403) in the FIG. 4 example.

In an HEVC example, the video encoder (703) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (703) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (703) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 7 example, the video encoder (703) includes the interencoder (730), an intra encoder (722), a residue calculator (723), aswitch (726), a residue encoder (724), a general controller (721), andan entropy encoder (725) coupled together as shown in FIG. 7.

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (722) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (721) is configured to determine general controldata and control other components of the video encoder (703) based onthe general control data. In an example, the general controller (721)determines the mode of the block, and provides a control signal to theswitch (726) based on the mode. For example, when the mode is the intramode, the general controller (721) controls the switch (726) to selectthe intra mode result for use by the residue calculator (723), andcontrols the entropy encoder (725) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(721) controls the switch (726) to select the inter prediction resultfor use by the residue calculator (723), and controls the entropyencoder (725) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (723) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (722) or the inter encoder (730). Theresidue encoder (724) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (724) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (703) also includes a residuedecoder (728). The residue decoder (728) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (722) and theinter encoder (730). For example, the inter encoder (730) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (722) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (725) is configured to format the bitstream toinclude the encoded block. The entropy encoder (725) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (725) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 8 shows a diagram of a video decoder (810) according to anotherembodiment of the disclosure. The video decoder (810) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (810) is used in the place of the videodecoder (410) in the FIG. 4 example.

In the FIG. 8 example, the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in FIG. 8.

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (872) or the inter decoder (880), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (880); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (872). The residual information can be subject to inversequantization and is provided to the residue decoder (873).

The inter decoder (880) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (872) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (873) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (873) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (871) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (874) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (873) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In an embodiment, the video encoders (403), (603),and (703), and the video decoders (410), (510), and (810) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

Aspects of the disclosure provide techniques for block basedcompensation from a same picture, specifically techniques forconstrained search range in intra picture block compensation.

Block based compensation can be used for inter prediction and intraprediction. For the inter prediction, block based compensation from adifferent picture is known as motion compensation. For intra prediction,block based compensation can also be done from a previouslyreconstructed area within the same picture. The block based compensationfrom reconstructed area within the same picture is referred to as intrapicture block compensation, or intra block copy. A displacement vectorthat indicates the offset between the current block and the referenceblock in the same picture is referred to as a block vector (or BV forshort). Different from a motion vector in motion compensation, which canbe at any value (positive or negative, at either x or y direction), ablock vector has a few constraints to ensure that the reference block isavailable and already reconstructed. Also, in some examples, forparallel processing consideration, some reference area that is tileboundary or wavefront ladder shape boundary is excluded.

The coding of a block vector could be either explicit or implicit. Inthe explicit mode, the difference between a block vector and itspredictor is signaled; in the implicit mode, the block vector isrecovered from a predictor (referred to as block vector predictor), in asimilar way as a motion vector in merge mode. The resolution of a blockvector, in some implementations, is restricted to integer positions; inother systems, the block vector is allowed to point to fractionalpositions.

In some examples, the use of intra block copy at block level, can besignaled using a reference index approach. The current picture underdecoding is then treated as a reference picture. In an example, such areference picture is put in the last position of a list of referencepictures. This special reference picture is also managed together withother temporal reference pictures in a buffer, such as decoded picturebuffer (DPB).

There are also some variations for intra block copy, such as flippedintra block copy (the reference block is flipped horizontally orvertically before used to predict current block), or line based intrablock copy (each compensation unit inside an M×N coding block is an M×1or 1×N line).

FIG. 9 shows an example of intra block copy according to an embodimentof the disclosure. Current picture (900) is under decoding. The currentpicture (900) includes a reconstructed area (910) (grey area) andto-be-decoded area (920) (white area). A current block (930) is underreconstruction by a decoder. The current block (930) can bereconstructed from a reference block (940) that is in the reconstructedarea (910). The position offset between the reference block (940) andthe current block (930) is referred to as a block vector (950) (or BV(950)).

According to some aspects of the disclosure, motion compensation basedtechniques can be suitably modified for the intra block copy.

In an example, pattern matched motion vector derivation (PMNIVD) mode isa technique that motion information of a block is not signaled butderived at both encoder and decoder side. Typically, there are twopattern matched motion vector derivation methods, bilateral matching andtemplate matching.

FIG. 10 shows an example of bilateral matching according to someembodiments.

As shown in FIG. 10, the bilateral matching is used to derive motioninformation of the current CU (1010) (in a current picture Cur Pic) byfinding the closest match between two blocks (1020) and (1030) along themotion trajectory of the current CU (1010) in two different referencepictures (Ref0 and Ref1). Under the assumption of continuous motiontrajectory, the motion vectors MV0 and MV1 pointing to the two referenceblocks (1020) and (1030) shall be proportional to the temporaldistances, i.e., TD0 and TD1, between the current picture (Cur Pic) andthe two reference pictures (Ref0 and Ref1). As a special case, when thecurrent picture is temporally between the two reference pictures and thetemporal distance from the current picture (Cur Pic) to the tworeference pictures (Ref0 and Ref1) is the same, the bilateral matchingbecomes mirror based bi-directional MV.

FIG. 11 shows an example of template matching according to an embodimentof the disclosure. As shown in FIG. 11, template matching is used toderive motion information of the current CU (1110) by finding theclosest match between a template (including a top and a left neighboringblocks (1120) and (1130) of the current CU (1110)) in the currentpicture (Cur Pic) and blocks (1140) and (1150) (same shape and size asthe template) in a reference picture (Rem).

In some examples, motion compensation is performed at block level, thatis, the current block is the processing unit for performing motioncompensation using the same motion information. Given the size of ablock, all pixels in the block will use the same motion information toform their prediction block.

In another example, a technique using block level merge candidates isused in motion compensation. The block level merge candidates caninclude spatial merge candidates and temporal neighboring positions. Inbi-directional prediction, the block level merge candidates can alsoinclude some combinations of motion vectors from existing mergecandidates.

FIG. 12 shows an example of spatial merge candidates. In the FIG. 12example, a current block (1201) comprises samples that have been foundby the encoder during the motion search process to be predictable from aprevious block of the same size that has been spatially shifted. Insteadof coding that MV directly, the MV can be derived from metadataassociated with one or more reference pictures, for example from themost recent (in decoding order) reference picture, using the MVassociated with either one of five surrounding samples, denoted A0, A1,and B0, B1, B2 ((1202) through (1206), respectively). Then, the MVprediction can use predictors from the same reference picture that theneighboring block is using. In the FIG. 12 example, the samples at thecurrent block's neighboring positions (1202)-(1206) are used for spatialmerge candidates.

In some examples of intra block copy implementations, block vector issignaled in explicit or implicit mode. The block vector in this contextis referred as signaled block vector. In some other examples of intrablock copy implementations, a current block can be predicted by areference block from the current block's spatial neighboring area whichhas been reconstructed. The displacement from this current block to itsreference is not signaled, but through a series of pattern matchingderivation. In an example, a region-based template matching method isused. In the example, several regions' shapes and sizes are assumed inthe reference area of the current picture by both encoder and decoder.At the decoder side, an index is parsed from the bitstream to select aregion. Then template matching is performed for all possible locationsinside the region. The reference location with a minimum matching costwill be used as the predictor for the current block. The block vectorfrom such derivation is referred as derived block vector. For the BVderivation process in a region, the starting point of the patternmatching, as well as the search order from one location to the next, arepre-defined and known by both encoder and decoder.

In consideration of some implementation cost, the reference area ofimmediate neighborhood of the current block may not be ready forpredicting the current block, or the use of these neighborhood datawould be expensive in terms of design. It is therefore desirable toconstraint the compensation range when intra block copy mode is usedsuch that the current block can only refer to a reference block that isoutside the constraint area.

There is a need to further improve the efficiency of intra block copywith a constrained reference area. In the present disclosure, there area few methods proposed to address such an issue.

According to some aspects of the disclosure, methods to improve intrablock copy applicability with certain constraints can be used. Morespecifically, block vector constraints are used in consideration of thespecified immediate neighborhood reference area that cannot be used forpredicting the current block. For example, a neighborhood area includingthe CTU to the left of current CTU (referred as left CTU for short) isconsidered as the immediate neighborhood. On top of that, a few methodscan be used to handle the excluded area without imposing block vectorconstraints.

In some embodiments, at a time to reconstruct a current block in a firstCTU in a picture according to the intra block copy mode, reconstructedsamples of certain neighboring area to the first CTU may not beavailable in a first memory that buffers the reconstructed samples ofthe current picture. For example, the first memory has a relativelylarge storage space and a relatively slow access speed, such as anoff-chip memory. The first memory can be accessed to retrieve thereconstructed samples in the reference area for the reconstruction ofthe current block. In some examples, a second CTU that is adjacent to aleft side of the first CTU, and is also referred to as left CTU forshort in some examples, is reconstructed just before the first CTU, andto store the reconstructed samples of the second CTU to the first memorytakes time. Thus, in some examples, the reconstructed samples of thesecond CTU are not available in the first memory at the time toreconstruct the current block in the first CTU.

In some embodiments, to avoid waiting time for storing the reconstructedsamples of the second CTU to the first memory, the reconstructed samplesof the second CTU are excluded from being reference samples for thereconstruction of the current block in the first CTU. According to anaspect of the disclosure, the second CTU is excluded from the referencearea for the reconstruction of the current block. According to anotheraspect of the disclosure, padding samples are used in the place of thereconstructed samples of the second CTU.

Specifically, in some implementation architecture, especially the CTUbased pipeline structure, the data in two consecutive CTUs of the sameCTU line is processed one CTU by one CTU. When coding samples of thecurrent CTU, the reference samples in the left CTU have just beenreconstructed and may not be ready to put into the memory that storesreference samples of the current decoded picture. Then, using thereference samples from the left CTU will cause processing delay of thepipeline processing.

According to an aspect of the disclosure, the allowed reference area forthe current block to perform intra block copy mode does not include thesamples from the left CTU.

FIG. 13 shows an example for excluding left CTU in the intra block copymode according to an embodiment of the disclosure. Current picture(1300) is under decoding. The current picture (1300) includes areconstructed area (1310) (grey area and dot area) and to-be-decodedarea (1320) (white area). A current block (1330) is under reconstructionby a decoder. The current block (1330) can be reconstructed from areference block (1340) that is in the reconstructed area (1310). Theposition offset between the reference block (1340) and the current block(1330) is referred to as a block vector (1350) (or BV (1350)).

In the FIG. 13 example, each big block is a CTU. The grey area is theavailable reference area for predicting current block using intra blockcopy. The left CTU (1360) (dot area) is excluded from the referencearea.

In some examples, the top left position of the current block isrepresented by (CUx, CUy), the origin is the top-left corner of thepicture. The block size is represented by (CUwidth, CUheight), whereCUwidth denotes the width of the current block (e.g., number of samplesin horizontal direction), and CUheight denotes the height of the currentblock (e.g., number of samples in vertical direction). The top leftposition of the current CTU (e.g., having the current block) isrepresented by (CTUx, CTUy). The size of the CTU is represented by(CTUwidth, CTUheight), where CTUwidth denotes the width of the CTU(e.g., number of samples in the horizontal direction), and CTUheightdenotes the height of the CTU (e.g., number of samples in the verticaldirection). The block vector is represented by (BVx, BVy), where BVxdenotes the horizontal component and BVy denotes the vertical component.

Accordingly, the top left corner of the reference block is representedby Ref_TL=(Lx, Ty)=(CUx+BVx, CUy+BVy). The top-right corner of thereference block is Ref_TR=(Rx, Ty)=(CUx+BVx+CUwidth−1, CUy+BVy). Thebottom-left corner of the reference block is Ref_BL=(Lx, By)=(CUx+BVx,CUy+BVy+CUheight−1), and the bottom-right corner of the reference blockis Ref_BR=(Rx, By)=(CUx+BVx+CUwidth−1, CUy+BVy+CUheight−1).

In some embodiments, in addition to reference area constraints thatshould be applied to intra block copy, the following additionalconstraints are also applied to exclude the left CTU from the referencearea. Specifically, the locations of all samples in reference blockshould be outside of the left CTU.

In an example, in addition to reference area constraints that should beapplied to intra block copy, Lx is required to be greater than or equalto CTUx (Lx>=CTUx). Then, samples in the left CTU do not satisfy theadditional requirement, and are excluded from the reference area. Theconstraint requirement can also be written as: CUx+BVx>=CTUx.

In another example, in addition to reference area constraints thatshould be applied to intra block copy, Rx is required to be less than asubtraction of CTUx and CTUwidth (Rx<CTUx−CTUwidth). Then, samples inthe left CTU do not satisfy the additional requirement, and are excludedfrom the reference area. The constraint requirement can also be writtenas: CUx+BVx+CUwidth−1<CTUx−CTUwidth.

In another example, in addition to reference area constraints thatshould be applied to intra block copy, By is required to be less thanCTUy (By<CTUy). Then, samples in the left CTU do not satisfy theadditional requirement, and are excluded from the reference area. Theconstraint requirement can also be written as CUy+BVy+CUheight−1<CTUy.

According to another aspect of the disclosure, pixel values in theCTU(s), such as the left CPU, that is excluded from the reference areaof the current block can be padded when the pixel values are used asreference samples for reconstruction of current block. The pixel valuesthat are padded are referred to as padding samples in some examples.

In some embodiments, when the samples in the left CTU are excluded frombeing the reference samples in the reference area, some valid pixelvalues are used to represent the reference sample values in thereference area. Thus, a block vector is allowed to point to thisexcluded area (e.g., left CTU). It is noted that the replacement samplevalues (padding samples) are not used to actually put into the memory orbuffer (e.g., the first memory) that stores the reference samples in theexcluded area, but to use as a replacement (reference samples) forpredicting the current block in intra block copy mode. When at least apart of the reference block is in the excluded area (e.g., left CTU),the missing reference samples will be replaced with the fill-in values.For example, while the real reconstructed samples of the left CTU iswritten to the first memory, the padding samples are determined and usedas reference samples in the place of the real constructed samples toreconstruct the current block. Thus, the decoder does not need to waitfor the reconstructed samples of the left CTU to be available in thefirst memory.

In one embodiment, the fill-in samples for each column in the left CTUwill be copied from the sample at the most adjacent reference line abovethe left CTU, that has the same vertical location as the column in theleft CTU.

FIG. 14 shows a diagram for padding pixel values of reference area inthe intro block copy mode according to an embodiment of the disclosure.FIG. 14 shows a plurality of CTUs, such as a current CTU (1410) (alsoreferred to as first CTU), a left CTU (1420) (also referred to as secondCTU), a left neighboring CTU (1440) to the left CTU (1420), and an aboveneighboring CTU (1430) to the left CTU (1420). At the time ofreconstructing a current block in the current CTU (1410) in the intrablock copy mode, samples of the left neighboring CTU (1440) and theabove neighboring CTU (1430) have been reconstructed and have beenstored in the first memory.

Using FIG. 14 as an example, the decoder can access the first memory toretrieve reconstructed samples in the above neighboring CTU (1430), suchas a bottom reference line (1435) of the above neighboring CTU (1430)and uses the retrieved samples to pad the left CTU (1420). In anexample, for each column in the left CTU (1420), pixels in the columnare padded with the same pixel values as a corresponding pixel in thebottom reference line (1435) that has the same vertical location as thecolumn.

In another embodiment, the fill-in samples for each row in the left CTUwill be copied from the sample at the right most reference line that isto the left of the left CTU, that has the same horizontal location asthe row in the left CTU.

Using FIG. 14 as an example, the decoder can access the first memory toretrieve reconstructed samples in the left neighboring CTU (1440), suchas a rightmost reference line (1445) and uses the retrieved samples topad the left CTU 1420. In an example, for each row in the left CTU 1420,pixels in the row are padded with the same pixel values as acorresponding pixel in the rightmost reference line 1445 that has thesame horizontal location as the row.

In another embodiment, at the time of reconstructing a current block inthe current CTU (1410) in the intra block copy mode, reconstructedsamples in the rightmost column (1425) of the left CTU (1420) has beenbuffered in a second memory, such as an on-chip memory that can beaccessed with high speed and can be retrieved without delay. Using FIG.14 as an example, the decoder can access the second memory to retrievereconstructed samples in the rightmost column (1425) of the left CTU(1420) and uses the retrieved samples to pad the left CTU (1420). In anexample, for each row in the left CTU (1420), pixels in the row arepadded with the same pixel values as a corresponding pixel in therightmost column (1425) that has the same horizontal location as therow.

In another embodiment, the fill-in samples for each column in the leftCTU will be copied from the vertical sample at the most adjacentreference line above the left CTU (e.g., reference line (1435)). Whenthe current block is in the first CTU row of a picture or slice or tile,thus the above neighboring CTU is not available, then the fill-insamples for each row in the left CTU will be copied from the horizontalsample at the right most reference line that is to the left of the leftCTU (e.g., reference line (1445)). When the current block is in thefirst two CTUs of the picture or slice or tile, none of the aboveneighboring CTU or the left neighboring CTU is available, some defaultvalues (e.g., constant values) will be used as the replacement samples.For example, a middle value in a range is used to pad the left CTU. Inan example, the middle value is generated by left shift 1 bit of the bitdepth, such as 1<<(bit depth−1), where bit depth denotes the bit depthof the sample. In 8-bit case, the default sample is 128.

In another embodiment, the fill-in samples for each row in the left CTUwill be copied from the horizontal sample at the right most referenceline that is to the left of the left CTU (e.g., reference line (1445)).When the current block is in the second column of the a picture or sliceor tile, then the fill-in samples for each column in the left CTU willbe copied from the vertical sample at the most adjacent reference lineabove the left CTU (e.g., reference line (1435)). When the current blockis in the first two CTUs of the picture or slice or tile, none of theabove neighboring CTU or the left neighboring CTU is available, somedefault values (e.g., constant values) will be used as the replacementsamples. For example, a middle value in a range is used to pad the leftCTU. In an example, the middle value is generated by left shift 1 bit ofthe bit depth, such as 1<<(bit depth−1), where bit depth denotes the bitdepth of the sample. In 8-bit case, the default sample is 128.

It is noted that while the present disclosure uses square shape CTU inthe examples, the proposed methods that use replacement samples in theexcluded area of left CTU can also be applied to other shapes ofexcluded reference area, such the current CTU and the left CTU.

FIG. 15 shows a flow chart outlining a process (1500) according to anembodiment of the disclosure. The process (1500) can be used in thereconstruction of a block coded in intra mode, so to generate aprediction block for the block under reconstruction. In variousembodiments, the process (1500) are executed by processing circuitry,such as the processing circuitry in the terminal devices (310), (320),(330) and (340), the processing circuitry that performs functions of thevideo encoder (403), the processing circuitry that performs functions ofthe video decoder (410), the processing circuitry that performsfunctions of the video decoder (510), the processing circuitry thatperforms functions of the intra prediction module (552), the processingcircuitry that performs functions of the video encoder (603), theprocessing circuitry that performs functions of the predictor (635), theprocessing circuitry that performs functions of the intra encoder (722),the processing circuitry that performs functions of the intra decoder(872), and the like. In some embodiments, the process (1500) isimplemented in software instructions, thus when the processing circuitryexecutes the software instructions, the processing circuitry performsthe process (1500). The process starts at (S1501) and proceeds to(S1510).

At (S1510), prediction information of a current block in a first CTU isdecoded from the coded video bitstream. The prediction information isindicative of intra block copy mode.

At (S1520), reconstructed samples of a second CTU that is the left CTUof the first CTU are excluded from being reference samples forreconstruction of the current block. In an example, the second CTU isexcluded from a search area (a reference area) for a block vector forprediction in the intra block copy mode. In another example, the secondCTU is not excluded, but pixels in the second CTU are padded withpadding samples.

At (S1530), a block vector is determined. In an example, the search areadoes not include the second CTU. In another example, the search areaincludes the second CTU with padding samples.

At (S1540), samples of the current block are reconstructed based on theblock vector and the exclusion of the reconstructed samples of the leftCTU. Then the process proceeds to (S1599) and terminates.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 16 shows a computersystem (1600) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 16 for computer system (1600) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1600).

Computer system (1600) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1601), mouse (1602), trackpad (1603), touchscreen (1610), data-glove (not shown), joystick (1605), microphone(1606), scanner (1607), camera (1608).

Computer system (1600) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1610), data-glove (not shown), or joystick (1605), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1609), headphones(not depicted)), visual output devices (such as screens (1610) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1600) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1620) with CD/DVD or the like media (1621), thumb-drive (1622),removable hard drive or solid state drive (1623), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1600) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1649) (such as, for example USB ports of thecomputer system (1600)); others are commonly integrated into the core ofthe computer system (1600) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1600) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1640) of thecomputer system (1600).

The core (1640) can include one or more Central Processing Units (CPU)(1641), Graphics Processing Units (GPU) (1642), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1643), hardware accelerators for certain tasks (1644), and so forth.These devices, along with Read-only memory (ROM) (1645), Random-accessmemory (1646), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1647), may be connectedthrough a system bus (1648). In some computer systems, the system bus(1648) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1648),or through a peripheral bus (1649). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1641), GPUs (1642), FPGAs (1643), and accelerators (1644) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1645) or RAM (1646). Transitional data can be also be stored in RAM(1646), whereas permanent data can be stored for example, in theinternal mass storage (1647). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1641), GPU (1642), massstorage (1647), ROM (1645), RAM (1646), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1600), and specifically the core (1640) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1640) that are of non-transitorynature, such as core-internal mass storage (1647) or ROM (1645). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1640). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1640) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1646) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1644)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

JEM: joint exploration modelVVC: versatile video codingBMS: benchmark set

MV: Motion Vector HEVC: High Efficiency Video Coding SEI: SupplementaryEnhancement Information VUI: Video Usability Information GOPs: Groups ofPictures TUs: Transform Units, PUs: Prediction Units CTUs: Coding TreeUnits CTBs: Coding Tree Blocks PBs: Prediction Blocks HRD: HypotheticalReference Decoder SNR: Signal Noise Ratio CPUs: Central Processing UnitsGPUs: Graphics Processing Units CRT: Cathode Ray Tube LCD:Liquid-Crystal Display OLED: Organic Light-Emitting Diode CD: CompactDisc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random AccessMemory ASIC: Application-Specific Integrated Circuit PLD: ProgrammableLogic Device LAN: Local Area Network

GSM: Global System for Mobile communications

LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB:Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: FieldProgrammable Gate Areas

SSD: solid-state drive

IC: Integrated Circuit CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video decoding in a decoder,comprising: decoding prediction information of a current block in afirst coding tree unit (CTU) in a picture from a coded video bitstream,the prediction information being indicative of an intra block copy mode;excluding reconstructed samples of a second CTU that is adjacent to aleft side of the first CTU in the picture from being reference samplesfor a reconstruction of the current block; and reconstructing samples ofthe current block based on reference samples that are in the picture andconstrained with the exclusion of the reconstructed samples of thesecond CTU.
 2. The method of claim 1, further comprising: excluding thesecond CTU from a reference area for providing the reference samples forthe reconstruction of the current block.
 3. The method of claim 1,further comprising: using padding samples to replace the reconstructedsamples of the second CTU as the reference samples for thereconstruction of the current block.
 4. The method of claim 3, furthercomprising: obtaining the padding samples without waiting for thereconstructed samples of the second CTU to be stored to a first memoryfor storing reconstructed samples of the picture.
 5. The method of claim4, further comprising: accessing the first memory for reconstructedsamples of a neighboring CTU to the second CTU to obtain the paddingsamples.
 6. The method of claim 5, further comprising: accessing thefirst memory for a bottom row of reconstructed samples of an aboveneighboring CTU to the second CTU; and padding rows of the second CTUrespectively according to the bottom row of the reconstructed samples ofthe above neighboring CTU.
 7. The method of claim 5, further comprising:accessing the first memory for a rightmost column of reconstructedsamples of a left neighboring CTU to the second CTU; and padding columnsof the second CTU respectively according to the right most column of thereconstructed samples of the left neighboring CTU to the second CTU. 8.The method of claim 4, further comprising: accessing a second memorythat buffers a rightmost column of the second CTU, the second memorybeing an on-chip memory that has a faster access speed than the firstmemory that is an off-chip memory; and padding columns of the second CTUrespectively according to the rightmost column of the second CTU.
 9. Themethod of claim 4, further comprising: padding the second CTU usingconstant values.
 10. An apparatus for video decoding, comprising:processing circuitry configured to: decode prediction information of acurrent block in a first coding tree unit (CTU) in a picture from acoded video bitstream, the prediction information being indicative of anintra block copy mode; exclude reconstructed samples of a second CTUthat is adjacent to a left side of the first CTU in the picture frombeing reference samples for a reconstruction of the current block; andreconstruct samples of the current block based on reference samples thatare in the picture and constrained with the exclusion of thereconstructed samples of the second CTU.
 11. The apparatus of claim 10,wherein the processing circuitry is further configured to: exclude thesecond CTU from a reference area for providing the reference samples forthe reconstruction of the current block.
 12. The apparatus of claim 10,wherein the processing circuitry is further configured to: use paddingsamples to replace the reconstructed samples of the second CTU as thereference samples for the reconstruction of the current block.
 13. Theapparatus of claim 12, wherein the processing circuitry is furtherconfigured to: obtain the padding samples without waiting for thereconstructed samples of the second CTU to be stored to a first memoryfor storing reconstructed samples of the picture.
 14. The apparatus ofclaim 13, wherein the processing circuitry is further configured to:access the first memory for reconstructed samples of a neighboring CTUto the second CTU to obtain the padding samples.
 15. The apparatus ofclaim 14, wherein the processing circuitry is further configured to:access the first memory for a bottom row of reconstructed samples of anabove neighboring CTU to the second CTU; and pad rows of the second CTUrespectively according to the bottom row of the reconstructed samples ofthe above neighboring CTU.
 16. The apparatus of claim 14, wherein theprocessing circuitry is further configured to: access the first memoryfor a rightmost column of reconstructed samples of a left neighboringCTU to the second CTU; and pad columns of the second CTU respectivelyaccording to the right most column of the reconstructed samples of theleft neighboring CTU to the second CTU.
 17. The apparatus of claim 13,wherein the processing circuitry is further configured to: access asecond memory that buffers a rightmost column of the second CTU, thesecond memory being an on-chip memory that has a faster access speedthan the first memory that is an off-chip memory; and pad columns of thesecond CTU respectively according to the rightmost column of the secondCTU.
 18. The apparatus of claim 13, wherein the processing circuitry isfurther configured to: pad the second CTU using constant values.
 19. Anon-transitory computer-readable medium storing instructions which whenexecuted by a computer for video decoding cause the computer to perform:decoding prediction information of a current block in a first codingtree unit (CTU) in a picture from a coded video bitstream, theprediction information being indicative of an intra block copy mode;excluding reconstructed samples of a second CTU that is adjacent to aleft side of the first CTU in the picture from being reference samplesfor a reconstruction of the current block; and reconstructing samples ofthe current block based on reference samples that are in the picture andconstrained with the exclusion of the reconstructed samples of thesecond CTU.
 20. The non-transitory computer-readable medium of claim 19,wherein the instructions further cause the computer to perform:excluding the second CTU from a reference area for providing thereference samples for the reconstruction of the current block.